<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml">
    <head>
       <meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
       <title>??</title>
       <style type="text/css">
          *{margin:0;padding:0;}
           .layer1{width:100%; height:100px; color:white;text-align:center;}
               .layer1-1{width:30%; height:100px; background:orange;color:blue;text-align:center;text-align:center;float:left;}
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                .layer1-3{width:30%; height:100px; background:yellow;color:blue;text-align:center;text-align:center;float:left;}
                .layer1-4{clear:both;}
           .layer2{width:100%; height:200px; background:lightgreen;color:blue;text-align:center;}
           .layer3{width:100%; height:200px;  background:pink;color:white;text-align:center;}           
       </style>
    </head>
    <body>
       <div class="layer1"> 
             <div class="layer1-1"></div>
             <div class="layer1-2"></div>
             <div class="layer1-3"></div>
             <div class="layer1-4"></div>
       </div>
       <div class="layer2"></div>
       <div class="layer3"></div>
    </body>
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